The present invention relates to a cassette type tape recorder to which a tape cassette accommodating a magnetic tape is applied, and more particularly relates to a mechanism by which a magnetic head is pulled out and withdrawn.
FIGS. 11 and 12 are plan views showing a conventional magnetic tape recording and playback device disclosed, for example, in Japanese Unexamined Patent Publication No. 60-113349. FIG. 11 is a view showing the condition of withdrawal, and FIG. 12 is a view showing the condition of advance in the case where the tape is recorded and played back.
Next, the operation will be explained as follows.
FIGS. 11 and 12 show a mechanism for moving a magnetic head mounting plate 102 from a withdrawal position (stopping position) to an advance position (acting position). A drive gear 189 is attached onto the reverse side of a primary base plate (not shown in the drawing) close to a gear 138. This drive gear 189 includes: a resting section 190 in which a portion of the gear is cut away; a spring receiving protruding section 191 formed on the upper surface side; a spiral rotary cam 192 provided on the lower surface side; and a stopping time engaging section 193 also provided on the lower surface side. A stopper wall 194 is protruded from a lower surface peripheral section of the drive gear 189. Further, an acting time engaging section 195 is protruded at a position close to the stopping time engaging section 193.
In this connection, a movable iron core 110a of a magnet plunger 110 is pushed in the extended direction by a coil spring 110b at all times. When a solenoid is energized with current due to the insertion of a cassette, the movable iron core 110a is withdrawn into the solenoid. In the drawings, numeral 196 is an engagement lever, one end of which is a cam engaging section 196a, and the other end of which is a plunger engaging section 196b. The plunger engaging section 196b is engaged with a fore end portion of the movable iron core 110a of the magnet plunger 110, and the cam engaging section 196a is disposed along the lower surface of the rotary cam 192. In the drawings, numeral 197 is a leaf spring (a rod spring may be used), the free end of which comes into pressure contact with the spring receiving protruding section 191 so that a torque is given to the drive gear 189 to rotate it counterclockwise in the drawings.
Further, in the drawing, numeral 198 is a cam lever, which is rotatably pivoted on the reverse side of the primary base plate. At one end of the cam lever 198, a cam follower 198a is provided coming into contact with the cam surface of the rotary cam 192. A rod spring 199, the modulus of elasticity of which is high, is attached to this cam lever 198, and a fore end portion of this rod spring 199 is engaged with a portion of the magnetic head mounting plate 102. In this connection, numeral 200 is a tension spring for returning the magnetic head mounting plate 102 from the acting position to the stopping position. By the resilient force of this tension spring 200, the cam follower 198a is pressed onto the cam surface of the rotary cam 192.
Therefore, at the stopping time, as illustrated in FIG. 12, the cam engaging section 196a of the engaging lever 196 is engaged with the stopping time engaging section 193, and the resting section 190 is opposed to the gear 138. A resilient force of the leaf spring 197 is activated on the spring receiving protruding section 191, so that a torque is given to the drive gear 189 to rotate it counterclockwise in the drawing. The cam follower 198a is located at a position where the radius of the rotary cam 192 is minimum. Consequently, the magnetic head mounting plate 102 is maintained at the withdrawal position (stopping position) by the action of the tension spring 200.
When a tape cassette is inserted into the device under the above condition, the solenoid of the magnet plunger 110 is energized with current, and the engaging lever 196 is rotated by the operation of the movable iron core 110a, so that the cam engaging section 196a is released from the stopping time engaging section 193, and the drive gear 189 is slightly rotated by the action of the leaf spring 197 and meshed with the gear 138. Therefore, the rotation of the gear 138, that is, the rotation of the motor is transmitted to the drive gear 189, and the drive gear 189 is rotated clockwise approximately by one revolution. During the rotation of the drive gear 189, the cam follower 198a is moved to the maximum radius portion of the rotational cam 192, and the cam lever 198 is greatly rotated, so that the magnetic head mounting plate 102 is moved to an advance position, resisting a force of the tension spring 200 (shown in FIG. 12). At this time, the cam engaging section 196a is engaged with the acting time engaging section 195, so that the drive gear 189 is stopped. However, the resting section 190 is opposed to the gear 138 again, and the leaf spring 197 comes into pressure contact with the spring receiving protruding section 191. Therefore, a torque is given to the drive gear 189 so as to rotate it counterclockwise. The device is maintained under the above condition.
In order to provide a stopping condition, an electric current supplied to the magnet plunger 110 may be stopped. Simultaneously when the electric current is stopped, the movable iron core 110a returns to the extended direction, and the cam engaging section 196a of the engaging lever 196 is released from the acting time engaging section 195. Therefore, the drive gear 189 is a little rotated by the action of the leaf spring 197, and the cam follower 198a drops to the minimum radius section of the rotary cam 192. Accordingly, the head panel 102 is returned to the stopping position by the action of the return spring 200.
In this connection, there is provided a mechanism (not shown in the present drawing); but illustrated in J60-113349 by which the rotary plates, are rotated and linked with the withdrawal motion of the magnetic head mounting plate 102, so that the right and left gears are separated from the adjacent gears. Therefore, simultaneously when the magnetic head mounting plate 102 is returned to its original position, the torque transmission path from the motor to both reel shafts, is interrupted.
Whereas the conventional magnetic tape recording and playback device is constructed in the above manner, the head mounting base plate is pulled in the withdrawal direction at all times, and when the head mounting base plate is advanced, its advancing direction is the same as the extending direction of the spring used for withdrawal of the head mounting base plate. Consequently, the more the head mounting base plate is pulled out, the more the pulling force to pull out the head mounting base plate is increased. When the head mounting base plate is pulled out, it is necessary to resist the force of the spring used for withdrawing the head mounting base plate. Accordingly, it is necessary to provide a spring having a very high modulus of elasticity. Therefore, in the case of tape recording and playback, it is necessary to pull out and hold the magnetic head mounting base plate, resisting the maximum spring force which includes the maximum tension of the head mounting base plate withdrawal spring, and the spring force corresponding to the deflection of the head mounting base plate pulling spring. The conventional device has the above problems.